OPSONIC POWER. 131 



ments, we should use a 5% emulsion of human red cells in salt solution, 

 to which has been added the inactivated serum of the animal immune 

 to human red cells. This immune serum should be capable of dis- 

 solving red cells in a dilution of at least i to 1000. 



Experiment. In a test-tube put 4 drops of the extract of syphilitic 

 liver and the same amount of the inactivated serum of the patient. 

 Now add i c.c. of a i-io dilution of guinea-pig serum and allow the 

 mixture to remain in the incubator at 37 C. for i hour. Then add 

 i c.c. of the sensitized 5% emulsion of red cells, and if haemolysis does 

 not take place, the patient has syphilis. Controls should not only be 

 made with serum from normal persons, but also extracts prepared from 

 normal livers should be used as well. This is one of the most exacting 

 of laboratory diagnostic tests. 



DETERMINATION OF OPSONIC POWER AND THE PREPARATION 

 OF VACCINES. 



The following modification of Irishman's method takes very little 

 time and skill and is applicable in the determination of the organism 

 concerned in an infection, as in Wright's method. The control of 

 vaccine treatment by taking opsonic indices from time to time does not 

 seem to have met with much favor in this country the sources of error 

 being as great, if not greater, than ordinary variations in the opsonic 

 index during the negative and positive phases. Method: Emulsify, 

 by repeatedly drawing up and ejecting with a bulb capillary pipette, a 

 small loopful of a young agar culture of the organism to be diagnosed 

 in 12 to 15 drops of salt solution containing i% of sodium citrate (the 

 citrate prevents coagulation). This may most conveniently be done 

 in a watch glass. Now puncture the ear of the patient and draw up 

 blood to a point marked on the capillary bulb pipette with a grease pen- 

 cil. Draw in air to make a slight break in the column and then draw 

 up bacterial emulsion to the same mark. Thoroughly mix the blood 

 and emulsion on a slide by drawing up and ejecting the mixture. 

 Then finally draw up the mixture to about 2 inches above the tip and 

 seal the tip off in the flame. Put the pipette preparation in the in- 

 cubator for exactly 15 minutes. Prepare a similar preparation, using 

 the blood of a normal person. At the expiration of 15 minutes' incu- 



